Piston having a barrel of forged steel and a cooling channel

ABSTRACT

A piston with a cooling channel having a basic piston barrel made from forged steel and a box-shaped shaft, bosses and boss supports and connecting walls between the boss supports as well as a combustion trough. The piston increases the rigidity of the ring part. To accomplish this, the piston has a wall extending all around above the boss bores. A structural component is welded in between the wall and the piston head and limits the cooling channel. This design increases the rigidity of the ring part in pistons.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to piston with a basic piston barrel offorged steel and a cooling channel. In particular, this inventionrelates to a piston in which deformation in the region of the ring bandis minimized.

2. The Prior Art

This type of a piston and a process for its manufacture are known fromGerman Patent No. 44 46 726 Al. However, the piston shown in this patenthas the drawback that the ring band is tied to the basic piston barrelonly via the piston head. Thus, the ring band is consequentlysusceptible to deformation.

A piston made of cast iron is known from PCT Application WO 80/02308,where the top part and the boss part are welded together. This pistonhas a rib extending all around above the bosses; however, this rib isnot welded to the top part and has no stiffening function.

Another piston of this type is shown in German Patent No. DE 24 34 902A, where sections of the ring band and a radially outward section of thepiston head are formed by a welded-in component. This measure, however,exclusively forms a cooling channel. This is a problem which has beensolved already in the relevant state of the art by closing the machinedcooling channel with a metal sheet.

Another piston is shown in German Patent No. DE 30 32 671 A, where a toppart made of heat-resistant steel and a bottom part made of flow-pressedsteel are welded together.

SUMMARY OF THE INVENTION

It is an object of the present invention to minimize deformation in theregion of the ring band of pistons of this type.

This and other objects of the invention are achieved by a pistoncomprising a basic piston barrel made of forged steel having a carbonequivalent of at least 0.3% and having a box-shaped shaft. There are acooling channel and bosses with boss bores and boss supports formed inthe piston barrel. The boss supports have connecting walls between them.There is a wall extending all around the piston barrel and disposedaxially above the boss bores. The wall extends radially outside of theboss supports and the connecting walls and is integrally formed with thebasic piston barrel. There is a combustion trough formed in the pistonbarrel.

In the piston according to the invention, at least part of the ring bandand piston head are formed by a structural component which is welded tothe basic barrel of the piston by two welding seams. The rigidity of thering section is therefore distinctly increased. The structural partforms at least part of a ring band and part of a piston head disposedoutwardly radially on the piston barrel. The welding seams are producedby MIG-welding, MAG-welding, laser welding or electron beam welding. Thewall of the basic piston barrel and the structural component jointlyform a radially outer and axially lower limiting wall of the coolingchannel, resulting in a bending-resistant zone in the region of the ringband.

In a preferred embodiment, there is an elastic metal sheet in theinterior of the piston, which forms a lower limitation of an innercooling space. The metal sheet is fixed in the region of the bosssupport by its own initial stress.

The box-shaped shaft can be separated from the ring band either by arecess in the pressure/counter-pressure direction as shown in thedrawings, or it can be connected with the ring band and the surroundingwall.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparentfrom the following detailed description considered in connection withthe accompanying drawing which discloses two embodiments of the presentinvention. It should be understood, however, that the drawing isdesigned for the purpose of illustration only and not as a definition ofthe limits of the invention.

In the drawing, wherein similar reference characters denote similarelements throughout the several views:

FIG. 1 shows a partial cross-sectional view of a piston as defined bythe invention;

FIG. 2 shows a different cross-sectional view of the piston shown inFIG. 1;

FIG. 3 shows a partial cross-sectional view of another embodiment of thepiston as defined by the invention; and

FIG. 4 shows a different cross-sectional view of the embodiment shown inFIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring in detail to the drawings, FIGS. 1-4 show piston 1, whichconsists of a basic piston barrel 2 and a structural component 3 weldedto barrel 2. Component 3 comprises part of the ring section and thepiston land as well as part of piston head 5. The ring portion and thepiston land are jointly denoted by reference numeral 4. A combustiontrough 6 is arranged in piston head 5. The basic piston barrel consistsof the bosses, which have a boss bore 7, boss supports 8 and connectingwalls 9 between the bosses. There is a wall 10 shaped by molding aboveboss bores 7 and extending all around and radially disposed outside ofthe bosses and the connecting walls 9 between the bosses. There is alsoa well as piston head 5 with combustion trough 6.

Wall 10, which runs all around, starts to extend from the bosses orconnecting walls between the boss supports and runs upwardly and isslanted radially to the outside.

The welding seams are in the form of an axial seam in the outer regionof the piston head, and in the form of a radial seam in the region ofthe ring band between the second and third grooves.

The box-shaped shaft 11 can be connected either only to the bosses oralso with ring band 4.

Wall 10 substantially forms a lower limitation of a cooling channel 12,and the welded-in structural component 3 substantially forms a radiallyouter limitation of cooling channel 12.

There is an elastic metal sheet 13 in the interior of the piston, whichforms a lower limitation of an inner cooling space. Metal sheet 13 isfixed in the region of boss support 8 by its own initial stress.

Accordingly, while only a few embodiments of the present invention havebeen shown and described, it is to be understood that many changes andmodifications may be made thereunto without departing from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. A piston comprising:a piston barrel made offorged steel having a carbon equivalent of at least 0.3% and having abox shaped shaft; a cooling channel formed in the piston barrel; bosseswith boss bores and boss supports formed in the piston barrel;connecting walls between the boss supports; a wall extending all aroundthe piston barrel and disposed axially above the boss bores, said wallextending radially outside of the boss supports and the connectingwalls, said wall being integrally formed with the basic piston barrel;an elastic metal sheet in the interior of the piston, said sheet forminga lower limitation of an inner cooling space, said metal sheet beingfixed in the region of the boss support by its own initial stress; acombustion trough formed in the piston barrel; and a structuralcomponent welded to the piston barrel and forming at least part of aring band and part of a piston head disposed outwardly radially on thepiston barrel, wherein the welding seams are produced by a processselected from the group consisting of MIG-welding process, MAG-weldingprocess, laser welding and electron beam welding; wherein the wall ofthe piston barrel and the structural component jointly form a radiallyouter and axially lower limiting wall of the cooling channel, resultingin a bending-resistant zone in the region of the ring band.